1. Technical Field
The present disclosure relates to a light emitting diode (LED) and a method for making the same.
2. Description of Related Art
In recent years, highly efficient LEDs made with GaN-based semiconductors have been widely applied in different technologies, for example in display devices, large electronic billboards, street lights, car lights, and other illumination applications. LEDs are environmentally friendly, and have long working life, and low power consumption.
A conventional LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active layer, an N-type electrode and a P-type electrode. The active layer is located between the N-type semiconductor layer and the P-type semiconductor layer. The P-type electrode is located on the P-type semiconductor layer. The N-type electrode is located on the N-type semiconductor layer. Typically, the P-type electrode is transparent. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, holes in the P-type semiconductor layer and electrons in the N-type semiconductor layer can enter the active layer and combine with each other to emit visible light.
However, extraction efficiency of LEDs is low because typical semiconductor materials have a higher refractive index than that of air. Large-angle light is light traveling at an angle defined between the light and a medium boundary. If the angle is larger than a particular critical angle, the light will be internally reflected. Large-angle light emitted from the active layer may be internally reflected in LEDs, so that a large portion of the light emitted from the active layer will remain in the LEDs, thereby degrading the extraction efficiency.
What is needed, therefore, is an LED which can overcome the above-described shortcomings.